In some cases android ROM prevent you from running adb as root. After an adb root you can get the message adbd cannot run as root in production builds which is super annoying.
The script ./adb_insecure.sh can patch any android ROM kernel in order to enable running adbd as root.
./adb_insecure.sh YOUR_ROM.zip
Then you will get a boot.img file that you can flash with fastboot flash boot boot.img in bootloader mode.
On Xioami.eu ROMS the ramdisk/default.prop is a symlink to /system/etc/prop.default.
You can if you want take that /system/etc/prop.default and overwrite the ramdisk/default.prop.
The script right now is simply overwriting the ramdisk/default.prop with a default one.